The present invention is based on a circuit arrangement for supplying electrical energy to a load.
German Patent Application No. 39 36 638 describes a circuit arrangement that ensures the supply of energy to electrical loads in an electrical system of a motor vehicle. By deactivating individual loads in controlled fashion, the vehicle voltage is prevented from dropping below a predefined value. This action ensures that the energy content of the motor vehicle battery is at least sufficient for a starting operation. In order to prevent excessively frequent activation and deactivation of individual loads when a threshold battery voltage value is reached, it is necessary to provide a hysteresis which ensures that after being deactivated, a load is not reactivated again until the voltage has risen by an amount equal to the hysteresis.
An object of the present invention is to provide a circuit arrangement for supplying electrical energy to a load that prevents the residual energy contained in a battery from dropping below a predefined quantity.
The circuit arrangement according to the present invention has the advantage that the energy stored in the battery can be made completely available for powering the loads until a predefined minimum battery voltage is reached. The fact that the circuit arrangement according to the present invention operates continuously prevents frequent complete activation and deactivation of the load.
The advantages are achieved by the fact that a controller is provided that regulates the battery voltage to the minimum battery voltage by delivering a manipulated variable, which defines the electrical power consumption of the load. A prerequisite is that the power of the load be controllable at least within predefined limits. If the circuit arrangement according to the present invention is arranged in a motor vehicle, such loads are, for example, a fan, an air conditioner, a refrigerator, a receiver of a remote control system or, for example, an alarm system. The minimum battery voltage that is to be defined is established in such a way that on the one hand the functionality of the load can still be maintained, and on the other hand a reserve still remains so that, for example in a motor vehicle, a starting operation can be performed.
A first advantageous embodiment provides for the power consumption of the load to be defined by a pulse-width modulation of the supply voltage of the load. The clock frequency is preferably defined in such a way that the load current flows as continuously as possible.
Another embodiment provides for the manipulated variable that defines the electrical power consumption of the load to be limited to a lower value. The limitation to a lower value can advisable in terms of the behavior of the load. Another considerable advantage is the fact that the voltage of the battery can largely be prevented from dropping below the predefined minimum battery voltage in the context of control fluctuations.
An advantageous embodiment provides for the minimum battery voltage to be influenced as a function of correction variables such as, for example, the battery temperature or the current flowing through the battery.
A preferred use of the circuit arrangement according to the present invention exists in a motor vehicle that has a vehicle electrical system with a battery. An air conditioner or at least one fan is provided, for example, as the load. A remote control system or an alarm system can also be provided as the load. These loads can be active while the vehicle is unoccupied, with no risk that the battery voltage will fall below the predefined minimum.